Fogged direct positive silver halide emulsions containing photographic sensitizing dyes derived from substituted salicylaldehydes

ABSTRACT

Cyanine and merocyanine photographic sensitizing dyes derived from substituted salicylaldehydes and light sensitive silver halide emulsions containing such dyes are disclosed. Also disclosed are certain reversible spiropyranmerocyanine dye systems, the stabilization of a dye in either the spiropyran form or the merocyanine form and observations of these photochromic materials when coated in polymeric matrices.

United States Patent Haase Dec. 2, 1975 541 FOGGED DIRECT POSITIVESILVER 2,944,896 7/1960 111661 1 96/139 HALIDE EMULSIONS CONTAINING a oe a PHOTOGRAPHIC SENSITlZING DYES 3,713,832 1/1973 Shiba et al. 96/139DERIVED FROM SUBSTITUTED SALICYLALDEHYDES Inventor: Jan Raymond Haase,Rochester,

Assignee: Eastman Kodak Company,

Rochester, NY.

Filed: Oct. 29, 1973' Appl. No.: 410,948

U.S. CI. 96/140; 96/1.6; 96/90 PC; 96/101; 96/139 Int. c1. 603C 1/22Field 61 Search 96/139, 140, 90 PC:1.6, 96/101 References Cited UNITEDSTATES PATENTS 11/1954 Butterfield 96/].5

Primary Examiner l. Travis Brown Attorney, Agent, or FirmM. R.Chipaloski [57] ABSTRACT Cyanine and merocyanine photographicsensitizing dyes derived from substituted salicylaldehydes and lightsensitive silver halide emulsions containing such dyes are disclosed.Also disclosed are certain reversible spiropyranmerocyanine dye systems,the stabilization of a dye in either the spiropyran form or themerocyanine form and observations of these photochromic materials whencoated in polymeric matrices.

l2v Claims, No Drawings FOGGED DIRECT POSITIVE SILVER HALIDE EMULSIONSCONTAINING PHOTOGRAPIIIC SENSITIZING DYES DERIVED FROM SUBSTITUTEDSALICYLALDEHYDES This invention relates to photographic silver halideemulsions containing sensitizing dyes derived from substitutedsalicylaldehydes.

In accordance with this invention there are provided photographic silverhalide emulsions containing a sensitizing dye represented by thefollowing general formulas:

and

wherein a is 0 or 1; R preferably represents a lower alkyl group having1 to 8 carbon atoms such as methyl, ethyl, propyl, butyl, etc., andincluding substituted lower alkyl groups such as a carboxyalkyl group(e.g., carboxymethyl, carboxyethyl, carboxypropyl, carboxybutyl, etc.),an alkoxycarbonyl alkyl group (e.g., methoxycarbonylmethyl,ethoxycarbonylethyl, propoxycarbonylethyl, propoxycarbonylbutyl, etc.),a sulfoalkyl group (e.g., sulfomethyl, sulfoethyl, sulfopropyl,sulfobutyl, etc.), a hydroxyalkyl group (e.g., hydroxymethyl,hydroxyethyl, hydroxypropyl, hydroxybutyl, etc.), an alkoxyalkyl group(e.g., methoxyethyl, methoxypropyl, ethoxyethyl, ethoxypropyl, etc.), asulfoalkoxyalkyl group, as well as an aryl group such as phenyl,4-methylphenyl, 4-chlorophenyl, etc.; R and R may be the same ordifferent groups and each represents hydrogen, a nitro group, a halogroup such as chloro, bromo, fluoro, or iodo, a lower alkoxy group suchas methoxy, ethoxy, propoxy, etc., or a lower alkyl group such aspreviously defined for R provided that at least one of the groups R, andR must be a nitro group or a halo group; and Z represents thenonmetallic atoms necessary to complete a heterocyclic nucleuscontaining from 5 to 6 atoms in the heterocyclic ring, such as aheterocyclic nucleus of the thiazole series (e.g., thiazole,4-methylthiazole, S-methylthiazole, 4- phenylthiazole, S-phenylthiazole,4,5-dimethylthiazole, 4,5-diphenylthiazole, 4-( 2-thienyl)thiazole,etc.), those of the benzothiazloe series (e.g., benzothiazole, 4-chlorobenzothiazole, 5-chlorobenzothiazole, 6- chlorobenzothiazole,7-chlorobenzothiazole, 4-methylbenzothiazole, S-methylbenzothiazole,6-methylbenzothiazole, S-bromobenzothiazole, 6-bromobenzothiazole,4-phenylbenzothiazole, S-phenylbenzo- 6-methoxybenzothiazole, 5-iodobenzo- .d]thiazole, etc.), those of the thieno[l,2-a1benzothiazoleseries (e.g., 5-methoxythieno[l,2-a]benzothiazole etc.), those of theoxazole series (e.g., 4- methyloxazole, S-r'nethyloxazole,4-phenyloxazole, 4,5- diphenyloxazole, 4-ethyloxazole,4,5-dimethyloxazole, S-phenyloxazole, etc.), those of the benzoxazoleseries (e.g., benzoxazole, S-chlorobe-nzoxazole, S-phenylbenzoxazole,5-methylbenzoxazole, 6-methylbenzoxazole, 5,6-dimethylbenzoxazole,4,6-dimethylbenzoxazole, 5-methoxybenzoxazole, 5-ethoxybenzoxazole, 6-chlorobenzoxazole, S-hydroxybenzoxazole, 6-hydroxybenzoxazole, etc.),those of the naphthoxazole series (e.g., naphth[2,1-d]oxazole,naphth[l,2-d]-oxazole, etc.), those of the selenazole series (e.g.,4-methylselenazole, 4phenylselenazo1e, etc.), those of the ben-Zoselenazole series (e.g., benzoselenazole, 5- chlorobenzosel'en'azole,S-methoxybenzoselenazole, 5-hydroxybenzoselenazole,tetrahydrobenzoselenazole, etc.), those of the naphthoselenazole series(e.g., naphtho[2,1-d]selenazole, naphtho[ l ,2-d]selenazole, etc.),those of the'thiazoline series (e.g., thiazoline, 4- methylthiazoline,etc.), those of the 2-quinoline series (e.g., quinoline,3-methylquinoline, S-methylquinoline, 7-methylquinoline,S-methylquinoline, 6-chloroquinoline, 8-chloroquinoline,6-methoxyquinoline, 6-ethoxyquinoline, 6-hydroxyquinoline,S-hydroxyquinoline, etc.), those of the 4-quinoline series (e.g.,quinoline, 6-methoxyquinoline, 7-meth ylquinoline, S-methylquinoline,etc.), those of the l-isoquinoline series (e.g., isoquinoline,3,4-dihydroisoquinoline, etc.) those of the 3,3-dialkylindolenine series(e.g., 3,3-dimethylindolenine, 3,3,5-trimethylindolenine,3,3,7-trimethylindolenine, etc.), those of the 2-pyridine series (e.g.,pyridine, 3-methylpyridine, 4-methylpyridine, S-methylpyridine,6-methylpyridine, 3,4-dimethylpyridine, 3,5- dimethylpyridine,3,6-dimethylpyridine, 4,5-dimethylpyridine, 4,6-dirriethylpyridine,4-chloropyridine, 5- chloropyridine, 6-chloropyridine,3-hydroxypyridine, 4-hydroxypyridine, S-hydroxypyridine,6hydroxypyridine, 3-phenylpyridine, 4-phenylpyridine, 6-phenylpyridine,etc.), those of the 4 pyridine series (e.g., 2- methylpyridine,3-methylpyridine, 2-chloropyridine, 3-chloropyridine,2,3-dimethylpyridine, 2,5-dimethylpyridine, 2,6-dimethylpyridine,2-hydroxypyridine, 3- hydroxypyridine, etc.), those of the imidazoleseries (e.g., imidazole, 4-methylimidazole, S-ethylimidazole,4-chloroimidazole, 4,5-dichloroimidazole, 4-methoxyimidazole,S-phenylimidazole, etc.), those of the benzimidazole series (e.g.,benzimidazole, 4-methylbenzimidazole, S-methylbenzimidazole,6-methylbenzimidazole, 5,6-dichlorobenzimidazole, S-chlorobenzimidazole,5-phenylbenzimidazole, 6-phenylbenzimidazole, etc.), those of thenaphthimidazole series (e.g., naphth[ l,2-d]imidazole,naphth[2,ld]imidazole, etc.), those of the lepidine series (e.g.,lepidine, 7-chlorolepidine, 7-methyllepidine, etc.).

The alkyl groups or moieties referred to herein typically have 1 to 20carbon atoms, lower alkyl radicals or moieties have 1 to 8 carbon atomsand aryl groups or moieties typically have 6 to 20 carbon atoms.

3 The dye compounds defined by Formulas l and II are prepared by heatinga mixture of a substituted salicylaldehyde having the formula wherein Rand R are as previously defined with a nitrogen-containing heterocycliccompound containing a reactive methyl group or a methylene grouprepresented by the general formulas wherein R, Z and a are as previouslydefined and A represents an anionic group such as chloride, bromide,iodide, p-toluenesulfonate, thiocyanate, perchlorate, acetate,methylsulfate, ethylsulfate, etc. The reaction is preferably conductedin an inert solvent such as tetrahydrofuran, pyridine, quinoline,isoquinoline, ethanol, propanol, butanol, etc., and in the presence of abasic condensing agent such as the trialkyl amines (e.g., triethylamine,tri-n-propylamine, tri-n-butylamine etc.), piperidine,N-methylpiperidine, N-ethylpiperidine, N, N-dimethylaniline, etc.

The following examples disclose the preparation of some of the dyes ofFormulas I and II:

EXAMPLE 1 1 ,3 '-Diethyl-2,3 -dihydro-6-nitrospiro( 2H)- 1-benzopyran-2,2 l H-imidazo[4,5-b]quinoxaline C 11 (If C ll5 A solutionof l,3-diethyl-2-methylimidazo[4,5- b]quinoxolium p-toluenesulfonate(4.12 g., .01 mole), 5-nitrosalicylaldehyde (1.67 g., .01 mole) andpiperidine (1.0 g.) in ethanol (30 ml.) is heated to reflux for minutes.During this period a dye crystallizes as green crystals and is collectedupon cooling. The yield of dye after washing with ethanol and ether anddrying is 2.4 g. (62% yield). The dye is refluxed in ethanol (130 ml.)containing 3 drops of triethylamine for 24 hours. The volume is thenreduced to 40 ml. After cooling, 1.75 g. (45% yield) of a pale greensolid is obtained, having a melting point of 2l5217C. Photocolorizationoccurs when a solution of this compound is irradiated with UV light.

EXAMPLE 2 6-[( 1-Methylnaphtho[ l,2-d]thiazolin-2-ylidene)ethylidene]-4-nitro-2,4-cyclohexadienone A mixture ofl,2-dimethylnaphtho[ l,2-d]thiazolium p-toluenesulfonate (3.85 g., 0.01mole), 5- nitrosalicylaldehyde (1.67 g., 0.01 mole) and piperidine (0.87g., 0.01 mole) is refluxed for 10 minutes in ethanol (25 ml.). The dyeprecipitates upon cooling and is collected and washed with ethanol togive 3.35 g. of product. A sample of 15g. of this crude product isdigested in dimethylformamide containing a small amount of ethanol. Thedye is collected and dried. The yield of dye is 1.4 g. yield) having amelting point of 243-245C. The dye can be reversibly bleached withvisible light.

Analysis: Calculated: C, 65.9%; H, 4.2%; N, 7.7%. Found: C, 66.2%; H,4.2%; N, 7.7%.

EXAMPLE 3 6-[( l-Ethylnaphtho[l,2,-d]thiazolin-2-ylidene)ethylidene]-4-nitro-2,4-cyclohexadienoneEXAMPLE 4 6[ 3-Ethyl-2-benzoselenazolinylidene )ethylidene 4-nitro-2,'4-cyclohexadienone CH-CHI N c 1 i A solution of3-ethyl-2-methylbenzoselenazolium ptoluenesulfonate (3.49 g., 0.01 mole)and 5- nitrosalicyladehyde (1.67 g., 0.01 mole) is prepared in ethanol(45 ml.) and filtered at room temperature. Piperidine (0.87 g., 0.01mole) is added andthe reaction mixture is heated for minutes. A solidprecipitates and is collected and washed with ethanol. The yield of dyeafter drying is 2.78 g. (75% yield having a melting point of 239C. Thedye can be reversibly bleached with visible light.

Analysis: Calculated: C 54.7%; H 3.8%; N 7.5% Found: C 54.4%; H 3.8%; N7.3%

EXAMPLE 6-[(l-Ethylnaphtho[2,3-d]thiazolin-2-ylidene)ethylidene]-4-nitro-2,4-cyclohexadienone A solution of l-ethyl-2-methylnaphtho[2,3-d]thiazolium p-toluenesulfonate (4.0 g., 0.01 mole) andS-nitrosalicyladehyde (1.67 g., 0.01 mole) in ethanol (100 ml.) isprepared and filtered at room temperature. Piperidine (0.87 g., 0.01mole) is added to the solution and the reaction mixture is refluxed forminutes. After cooling, the dye is collected and washed with ethanol.This provides 2.5 g. of product. This material is dissolved in m-cresolwith slight warming and filtered hot. Boiling methanol is then addeduntil the dye begins to crystallize. After cooling, the dye iscollected, washed and dried. The yield of dye is 0.9 g. (24% yield)having a melting point of 207 209C.

Analysis: Calculated: C, 67.0%; H, 4.3%. Found: C, 67.0%; H, 4.6%.

PEXAMPLE 6 Photocoloration is observed when solutions of this compoundare irradiated with UV light.

EXAMPLE 7 (1.67 g., 0.01 mole) and piperidine (0.87 g.) is refluxed inethanol 15 ml.) for one hour. Upon cooling, the dye precipitates and iscollected, washed with ethanol and dried. This provides 2.86 g. of dye.The material is recrystallized once from dimethylformamide to obtain 10g. of dye having a melting point of27lC. (dec.). Color changes areobserved when solutions of this dye are irradiated.

Analysis: Calculated: C, 67.6%; H, 5.7%; N 12.5%. Found: C, 67.5%; H,6.0%; N 12.4%.

EXAMPLE 8 6-[(3-Ethyl-2-benzoxazolinylidene)ethylidene1-4- nitro-2 ,4-cyclohexadieneone =CHCH A mixture of 3-ethyl-2-methylbenzoxazolium iodide(2.89 g., 0.01 mole), 5-nitrosalicylaldehyde (1.67 g., 0.01 mole) andpiperidine (1.0 g.) is refluxed in tetrahydrofuran (75 ml.) for 20minutes. The dye precipitates and after cooling is collected, washedwith tetrahydrofuran and dried. This provides 2.4 g. of dye. Thismaterial is digested in water, .collected and dried. This solid is thenrecrystallized from rn-cresol-methanol to obtain 1.87 g. yield) of dyehaving a melting point of 228230C. Solutions of the dye can bereversibly photobleached with visible light.

EXAMPLE 9 I 6-[( l-Ethy1-4(-1H)-quinolylidene)ethylidene]-4-nitro2,4-cyclohexadienone This dye is' prepared by the proceduredescribed in Example 3 in an 88% yield. The product has a melting pointof 260262C. I Analysis: Calculated: C, 71.2%; H, 5.0%. Found: C, 7 H;5.1%..-

EXAMPLE l6-[(3-Ethylnaphtho[2,l-d]thiazolin-2-ylidine)ethylidene]-4-nitro-2,4-cyclohexadienoneS This dye'is prepared by the procedure described in Example in a 75%yield. The product has a melting point of 239-240C. and is photoactive.

EXAMPLE 1 l 6-[ (5 ,6-Dichlorol,3-diethyl-2-benzimidazolinylidene)ethylidene1-4-nitro-2,4-cyclohexadienoneThis dye is prepared by the procedure described in Example 3 in an 86%yield. The product has a melting point of 292-294C. (dec.) and isphotoactive.

Analysis: Calculated: C, 58.8%; H, 4.4%. Found: C, 58.6%; H, 4.4%.

EXAMPLE l2 6[(3,4-Diphenyl-4-thiazolin-2-ylidene)ethylidene14-nitro-2,4-cyclohexadienone This dyeis prepared by the proceduredescribed in Example 7 except that the product is recrystallized fromethanol. The product is obtained in a 19% yield, has a melting point ofl92l97C. and is photoactive.

EXAMPLE l3 6-[( l-Methyl-2( lHl-quinolylidene)ethylidene]-4nitro-2,4-cyclohexadienone This dye is prepared by the procedure described inExample 3 in an 82% yield. The product has a melting point of 250253C.

Analysis: Calculated: C, 70.6%; H, 4.6%. Found: C, 70.5%; H, 4.6%.

EXAMPLE l4 6-[3-Ethyl-2-benzothiazolinylidene)ethylidene1-4nitro-2,4-cyclohexadienoneThis dye is prepared by the procedure desribed in Example 3 in a 72.5%yield. The product has a melting point of 235240C. and is photoactive.

Analysis: Calculated: C, 62.6%; H, 4.3%. Found: C, 62.7%; H, 4.4%. I i

p EXAMPLE 6-[( l ,3-Diethyll H-imidazo-[4,5-b]quinoxalin-2(3H)ylidene)ethylidene]-2-methoxy-4-nitro-2,4- cyclohe xadienone Thisdye is prepared by the procedure described in Example 5 in a yield.'Theproduct has a melting point of 241C. and is photoactive.

Analysis: Calculated: C, 63.0%; H, 5.0%.

Found: C, 62.6%; H, 5.2%.

EXAMPLE l6 6-[(3-Ethyl-2-benzothiazolinylidene)ethylidene1-2-methoxy-4-nitro-2,4-cyclohexadienone This dye is prepared by theprocedure described in Example 3 in a 50% yield. The product has amelting point of 242244C.

Analysis: Calculated: C, 60.7%; H, 4.5%. Found:C, A

EXAMPLE 17 6-[( l-Methylnaphtho[ l,2-d]-thiazolin-2-ylidene)ethylidene]-2-nitro-2,4-cyclohexadienone This dye is prepared by theprocedure described in Example 3 in an yield. The product has a meltingpoint of 202206C. and is photoactive.

Analysis: Calculated: C, 66.3%; H, 3.9%. Found: C, 66.0%; H, 4.0%.

EXAMPLE l8 6-[(3-Ethyl-2-benzothiazolinylidene )ethylidene1-2-nitro-2,4-cyclohexadienone This dye is prepared by the proceduredescribed in Example 7 except that the product is recrystallized inethanol. The product is obtained in a 16% yield, has a melting point ofl9ll93C. (dec.), and is photoactive.

Analysis: Calculated: C 62.6%; H, 4.3%. Found: C, 62.6%; H, 4.3%.

EXAMPLE l9 3 ,5-Dibromo-6- 3-ethyl- 2-benzothiazolinylidene)ethylidene]-2 ,4-cyclohexadienone This dye is prepared by the proceduredescribed in Example 3 in an 85% yield. The product has a melting pointof l94196C.

Analysis: Calculated: C, 48.2%; H, 3.1%. Found: C, 47.9%; H, 3.3%.

EXAMPLE 2l 6-[( l-Methylnaphtho[ l,2-d]thiazolin-2-ylidene)ethylidene]-2,4-dinitro-2,4-cyclohexadienoneThis 'dye is prepared by the procedure described in Example 5 in a 36%yield. The product has a melting point of 303C. (dec.) and isphotoactive.

Analysis: Calculated: C, 59.0%; H, 3.2%. Found: C, 59.1%; H, 3.3%.

EXAMPLE 22 6-[ 5 ,6-Dichlo rol,3-diethyl-2-benzimidazolinylidene)ethylidene]-2,4-dinitro-2,4-cyclohexadienone This dye is prepared by the procedure described inExample 5 in a 6% yield. The product has a melting point of 325C. (dec.)and is photoactive.

Analysis: Calculated: C, 50.6%; H, 3.6%. Found: C, 50.9%; H, 3.7%.

EXAMPLE 23 4-Nitro-6-[ 4,5 ,6,7-tetrachlorol ,3-diethyl-2-benzimidazolinylidene)ethylidene]-2,4-cyclohexadienone Thisdye is prepared by the procedure described in Example 3 in a 50% yield.The product has a melting point of 250C. (dec.) and is photoactive.

9 Analysis: Calculated: C, 48.0%; H, 3.2%. Found: C, 48.2%; H, 3.5%.

EXAMPLE 246-[(3-Ethyl-4-phenyl-4-thiazolin-2-ylidene)ethylidene1-4-nitro-2,4-cyclohexadienoneThis dye is prepared by the procedure described in Example 3 in a 90%yield. The product has a melting point of 22l222C. (dec.) and isphotoactive.

Analysis: Calculated: C, 64.8%; H, 4.6%. Found: C, 64.7%; H, 4.5%.

EXAMPLE 25 6-[( l,2-Dihydropyrrolo[2, 1 -b ]benzothiazol-3-yl)methylene]-4-nitro-2,4-cyclohexadienone This dye is prepared by theprocedure described in Example 3 in a 65% yield. The product has amelting point of 254255C.

Analysis: Calculated: C, 62.9%; H, 3.7%. Found: C, 62.6%; H, 3.7%.

EXAMPLE 26 6- 2,3-Dihydrol H-pyrido 2 l-b ben zothiazol-4-yl)methylene]-4-nitro-2,4-cyclohexadienone This dye is prepared by theprocedure described in Example 3 in a 54% yield and is digested inethanol. The product has a melting point of 234-239C. (dec.).

EXAMPLE 27 6-[( 1-Ethylnaphtho[ l,2-d]thiazolin-2-ylidene)ethylidene]-2,4-dinitro-2,4-cyclohexadienone This dye is prepared bythe procedure described in Example 3 in a 39% yield. The product has amelting point of 308309C. and is photoactive.

EXAMPLE 28 2,4-Dibromo-6-[( l-ethylnaphtho[ 1,2-d ]thiazolin-2-ylidene)ethylidene]-2,4-cyclohexadienone This dye is prepared by theprocedure described in Example 5 in a 75% yield. The product has amelting point of 190C. and is photoactive.

EXAMPLE 29 3,5-Dichloro-6-[( l-ethylnaphtho[ l ,2-d ]thiazolin-2-ylidene)ethylidene]-2,4-cyclohexadienone This dye is prepared by theprocedure described in Example 3 in a 53% yield. The product isrecrystallized from a mixture of dimethyl formamide, methanol andhexane. The product has a melting point of 2l5-2l7C. and is photoactive.

EXAMPLE 30 3 ,5-Dichlo ro-6-[ 3-ethylnaphtho 2, l -d ]thiazolin-2-ylidene)ethylidene]-2,4-cyclohexadienone This dye is prepared by theprocedure described in Example 30 in a 50% yield. The product has amelting point of 217C. and is photoactive.

EXAMPLE 3 1 3,5-Dichloro-6-[(3-ethyl-Z-benzothiazolinylidene)ethylidene]-2,4-cyclohexadienoneThis dye is prepared by the procedure described in Example 5 in a 58%yield. The product has a melting point of l42148C. and is photoactive.

EXAMPLE 32 3 ,5-Dichloro-6- 3-methyl-2-benzothiazolinylidene )ethylidene-2 ,4-cyclohexadienone This dye is prepared by the procedure describedin Example 1 l in a 42% yield. The product has a melting point of 2l6217C. and is photoactive.

EXAMPLE 33 6,8-Dibromo-l ',3 '-diethyl-2 ',3 '-dihydrospiro[ 2H]- 1benzopyran-2,2 1H )-imidazo[4,5-b]quinoxaline This dye is prepared bythe procedure described in Example 3 in a 36% yield. The product isrecrystallized from methylene chloride, has a melting point of l36l37C.and is photoactive.

EXAMPLE 34 6-[( l-Ethylnaphtho[l,2-d]thiazolin-2-ylidene)ethylidene]-2-methoxy-5-nitro-2,4-cyclohexadienoneThis dye is prepared by the procedure described in Example 3 in a 40%yield. The product is recrystallized from a mixture of dimethylformamide and ethanol. The product has-a melting point of 240-24lC. andis photoactive.

EXAMPLE 35 6-[(3-Ethylnaphtho[ 2, l-d]thiazolin-2-ylidene)ethylidene]-2-methoxy-5-nitro-2,4-cyclohexadienoneThis dye is prepared by the procedure described in Example 1 1 in a 59%yield. The product has a melting point of 239C. and is photoactive.

EXAMPLE 36 2-Methoxy-6-[( l-methyl-naphtho[ l ,2-d]thiazolin- Zylidene)]-4-nitro-2,4-cyclohe xadienone This dye is prepared by the proceduredescribed in Example 3 in a 97% yield. The product has a melting pointof 251-254C.

Analysis: Calculated: C, 64.3%; H 4.1%. Found: C, 64.5%; H 4.31%.

Depending upon the nature of the nitrogen-containing heterocyclicnucleus, i.e., the group the dyes at ambient temperatures exist ineither the merocyanine open colored form of Formula I or the closedcolorless spiropyran form of Formula II. Regardless of which form theyare in at ambient temperatures, they generally may be converted to theother form. Thus, these dyes exhibit extremely efficient photochromicbehavior. By control of the dye structure and the exciting wavelength,the dyes may be used in either negative or positive silver halidephotographic systems. The dyes of Formula] are particularly useful asspectral sensitizers for direct positive silver halide photographicsystems and for organic photoconductors.

Photographic silver halide emulsions which can be spectrally sensitizedby the dyes of this invention can comprise, for example, silverchloride, silver bromide, silver bromoiodide, silver chlorobromide,silver chloroiodide, silver chlorobromoiodide crystals or mixturesthereof. Suitable emulsions are described in Product Licensing Index,Volume 92, December 1971, Publica- 1 1 tion 9232, page 107, Paragraph I.

The silver halide emulsions can be unwashed or washed to remove solublesaltsafter precipitation of the silver halide as described in theaforementioned Product Licensing Index reference at page 107, ParagraphII. g I

The dyes of this invention are advantageously incorporated in thewashed, finished emulsion and should be uniformly distributed throughoutthe emulsion. The dyes can be added from solutions in appropriatesolvents which are compatible with the emulsion and which aresubstantially free from deleterious effects on the light sensitivematerials.

The types of silver halide emulsions that can be sensitized with the newdyes of this invention include those prepared with hydrophilic colloidsthat are known to be satisfactory vehicles for dispersed silver halidesas described in the aforementioned Product Licensing Index reference atParagraph VIII.

The concentration of the new dyes in the emulsion can vary widely, e.g.,from about 5 to 100 mg. per liter of flowable emulsion containing, forexample, 50 g. of silver bromide per liter. The specific concentrationwill vary according to the type of light-sensitive material in theemulsion and the effects desired. The suitable and most economicalconcentration for a given emulsion will be apparent to those skilled inthe art upon making the tests and observations customarily used in theart of emulsion making.

To prepare a gelatin-silver halide emulsion sensitized with one of thedyes of this invention, the following procedure is satisfactory. Aquantity of the dye is dissolved in a suitable solvent and a volume ofthis solution containing from 5 to 100 mg. of dye is slowly added to oneliter of a gelatin-silver halide emulsion. With most of the dyes, to mg.of dye per liter of emulsion suffices to produce the maximim sensitizingeffect with the ordinary gelatin-silver bromide (including bromoiodideand chlorobromide) emulsions. With fine grain emulsions, which includemost of the ordinarily employed gelatin-silver chloride emulsions,somewhat larger concentrations of dye may be necessary to obtain theopt'finum sensitizing effect. While this procedure has dealt withemulsions comprising gelatin, it will be appreciated that these remarksapply generally to any emulsion wherein all or part of the gelatin issubstituted by another suitable hydrophilic colloid as mentioned above.

Photographic silver halide emulsions containing the sensitizing dyes ofthis invention can also contain other addenda such as chemicalsensitizers, e.g., reducing agents; sulfur, selenium or telluriumcompounds; gold, platinum or palladium compounds; or combinations ofthese. Procedures for chemically sensitizing silver halide emulsions aredescribed in Sheppard et al. U.S. Pat. No. 1,623,499 issued Apr. 5,1927; Waller et al. U.S. Pat. No. 2,399,083 issued Apr. 23, 1946;McVeigh U.S. Pat. No. 3,297,477 issued Jan. 10, 1967 and Dunn U.S. Pat.No. 3,297,446 issued Jan. 10, 1967. The emulsions can containdevelopment modifiers that function as speed increasing compounds suchas polyalkylene glycols, cationic surface active agents and thioethersor combinations of these as described in Piper U.S. Pat. No. 2,886,437issued May 12, 1959; Dann et al U.S. Pat. No. 3,046,900 issued July 12,1960 and Goffe U.S. Pat. No. 3,294,540 issued Dec. 27, 1966.

The silver halide emulsions can be protected against the production offog and can be stabilized against loss 12 of sensitivity during keeping.Useful antifoggants and stabilizers are listed in the aforementionedProduct Licensing Index reference at Paragraph V.

The photographic silver halide emulsions of this invention can be coatedon a wide variety of supports. Typical supports include cellulosenitrate film, cellulose acetate film, poly( vinyl acetal) film,polystyrene film, poly(ethylene terephthalate) film, polycarbonate filmand related films or resinous materials, as well as glass, paper, metaland the like. Typically, a flexible support is employed, especially apaper support, which can be partially acetylated or coated with barytaand/or an alpha-olefin polymer, particularly a polymer of analpha-olefin containing2 to 10 carbon atoms such as polyethylene,polypropylene, ethylenebutene copolymers and the like.

Photographic elements having silver halide emulsions coated thereon cancontain developing agents such as those listed in the aforementionedProduct Licensing Index reference at Paragraph VI. The emulsions layerscan be hardened by various organic or inorganic hardeners, alone or incombination, such as those disclosed in the aforementioned ProductLicensing Index reference at Paragraph VII.

The photographic layers of this invention may also include other addendaknown to be beneficial in photographic emulsions such as those listed inthe Product Licensing Index reference at Paragraphs IV, XI, XII andXIII.

EXAMPLE 37 The sensitizing effects of several of the dyes describedabove are illustrated in the following tabulation where the sensitizingrange and sensitizing minimum values are shown for these dyes. The dyesare tested in a bromoiodide direct positive emulsion containing 2.5 molepercent iodide and having an average grain size of 0.2 micron asdescribed in Berriman U.S. Pat. No. 3,367,778. The dyes, dissolved insuitable solvents are added to separate portions of the emulsion at theconcentrations indicated. The emulsions are chemically fogged and arecoated at a coverage of mg. of silver per square foot on a cellulose.acetate film support. A sample of each coating is exposed on an Eastman1B Sensitometer, processed for 6 minutes in an Elonhydroquinonedeveloper, fixed, washed and dried. The photographic results from thesetests are set forth in Table I.

TABLE I Dye Concentration The dyes of Examples 1 to 7, 9 to 12 and 14are tested in a silver bromoiodide emulsion containing 2.5 mole percentiodide and having an average particle size 13 of 0.2 micron. The dyes,dissolved in suitable solvents, are added to separate portions of theemulsion at the concentrations indicated in Table II. The "emulsions aredigested at 40C. for 10 minutes and coated at a cover- EXAMPLE 39 Aspreviously noted, the merocyanine dyes of Formula I and the spiropyrancompounds of Formula II exage of 100 mg. of silver per square foot on acellulose hibit photochromic behavior. To illustrate this effect,aacetate film support. A sample of each coating is then various, testsare conducted on the compounds shown exposed to a mercury vapor lamp fora 365 nm emisin Table III. The tests are carried out in test tubes atsion on a spectrophotometer to obtain the sensitizing room temperatureusing a 200 watt Xenon flash lamp. range. The coatings are processed to6 minutes in an In most cases, photobleaching is more efficient whenElon-hydroquinone developer, fixed, washed and an ultraviolet filter isplaced between the lamp and the dried. The photographic results fromthese tests are set sample. Table III sets forth the photochromicproperforth in Table II. ties of the dyes tested in various solvents.The notation decolorized indicates that the dye is photobleached. TABLEII 4 For most of the dyes, the values for A and E X 10 99 are determinedat the time the solution is prepared and (mg/mole of silver tizingDesensltlzatlon 1 Example halide) Range (nm) in Lo E Units agaln after24 hours. In the last 4 columns of Tab e III, we to 484 27 the numbersin parentheses are the values for E X 10 2 100 to 480 and the numberswhich are not in parentheses are the i 200 I9 470 values of A Thenotation s following a value for 5 {3g 22 3% 20 k indicates the presenceof a shoulder on a larger 6 100 I0 485 .01 absorption band. 3 :38 23 :2;F In all cases the 24 hour reading represents the posi- 10 100 to 435 30tion of thermodynamic equilbrum. In many cases while 11 the dye form wasisolated the solution equilibra in- 12 100 to 490 25 volves somespiropyran (colorless) form. 14 100 16 485 .35

TABLE III 10% M-Cresol- Photoactivity Pyridine Ethyl Alcohol Dye ofExample Number Methanol Pyridine Initial After 24 hrs. Initial After 24hrs.

1 color color spiropyran 525 (0.23)

forms forms stable 2 decolordecolor 570 not soluble 5 10 (2.95) 510(2.83)

ized ized dye stable 3 decolordecolor- 570 5.13) 570 4.95 513 3.08 513(2.47

ized ized dye stable dye stable 4 decolob decolor- 570 (3.69). 570 (2.91522 (2.91) 522- 1.94)

ized ized mostly dye some dye 14 f decolordecolor- 565 424 563 (1.45)511 (3.08) 511 (3.02)

ized ized mostly spiropyran mostly dye at equilibrum 5 decolordecolor-582 (2.84) 582 (0.08 533 3.69 533 3.09)

ized ized allspiropyran all dye at equilibrum 10 decolordecolor- 575(3.44) 575 3.10) 518 (2.03) 518 (1.85

(ized. ized mostly dye mostly dyc 12 Inc .decolor- 553 (3.40 553 (3.29)502 1.54 502 1.37)

(change ized all dye all dye change change all dye all dye I 10 I10 I Ino 541 (3.69), 541 (3.69 480 2.31) 480 2.27) change change i g g 5 i alldyc I all dye 13 n6 no 573 4.75 572 (2.46) 508 (2.88) 508 (2.77

change I change some spiropyran 7 all dye .12 no N no 518(3.46)*''518(3;14 Y 457 (2.08) 45701.84) r change change 1 TABLE Ill-continuedM": X 10% M-Cresol- Photoactivity Pyridine 90% Ethyl Alcohol Dye ofExample Number Methanol Pyridine lnitial After 24 hrs. Initial After 24hrs.

7 v v 7 all dye mostly dye 11 color color 496 (2.09) 510s(0.82) 426(2.25) 415 (2.25)

change change 445 (2.25). 438 (2.56)

409 (2.13) undergoes cis-trans isomerism 7 color color 441 (2.61) 438(2.81) 427 (1.67) 417 (1.60) V change change change in 395s( 1.55)

curve shape undergoes cis-trans isomerism 37 no no change change 592(3.51) 592 (3.45) 541 (2.53) 541 all dyc color color 609 (0.14) 561(2.98) 561 (0.84) 15 generated generated I all spiropyran all spiropyran16 no no 589 (4.51) 589 (4.21) 541 (3.31) 541 change change all dye l8decolorized 19 no no 605 (3.83) 605 (3.51) 552 (2.50) 552 change changemostly dye 20 color decolor- 544 (4.81) 544 (0.65) 492 (1.56) 492 (1.17)

change ized mostly spiropyran mostly dye 21 not decolor- 535 (3.66) 535(3.18) 491 (2.63) 49ls(0.98)

soluble ized mostly dye mostly spiropyran or decomposition Dye Numbers 7and 11 are not decolorized but definite changes in color are observed.Dye Number 15 gives an initially weak colored solution, the color beingintensified by flashing in the absence of an ultraviolet filter. Thefailure of photobleaching to occur in Dye Numbers l5, l6 and 37 may becaused by a very rapid thermal return in these systems. The 2-methoxygroup appears to be responsible for this effect. The most efficientcompounds in the photobleaching reactions are those derived fromS-nitrosalicylaldehyde and which contain S-member heterocyclic nuclei.The data in Table 111 indicates that the dye form is generally morestable when the heterocyclic nuclei become more basic.

The following examples illustrate the behavior of dyes in polymers ofvarying polarity and the effect of metal ions and metal chelates,particularly of the rare earth series, on stabilizing the dye in eitherthe merocyanine or the spiropyran form:

EXAMPLE 40 This example employs Dye Number 1 of Table 111 which in mostpolymers and solutions exists as the closed (colorless) spiropyran andforms the intensely colored merocyanine (blue-purple) when exposed tolight with a wavelength of less than 400 nm. The colored form is rapidlybleached by light of wavelength greater than 400 nm. A solution of thedye, dissolved in pyridine, is added to a 10% solution of a butylacrylate-50% styrene copolymer in ethyl acetate, so as to give a 10 Mconcentration of the dye in the polymer solution. The resulting highlycolored solution fades to colorless shortly after mixing. The solutionis hand-coated on a conductive polyethylene terephthalate "film base ata knife setting of 0.008 inches under red safelights, then air dried. Aportion of this coating isexposed to an ultraviolet lamp watts) for 15seconds through a resolving-power chart (etched chrome plated quartzglass). The exposed area of the coating becomes a deep purple, giving anexcellent color negative. This negative image can be bleachedimmediately to give the colorless spiropyran by exposure to light from aphotollood lamp watts) of a wavelength greater than 400 nm or byexposure for 15 minutes under conditions of normal lighting (about 100ft. cdls.). The re-exposure of the resulting colorless film toultraviolet light intensifies the previously unexposed areas with thebackground considerably less colored. This image appears as a positiveand indicates some dye fatigue after the first exposure to ultravioletlight. This latent image positive can be repeatedly intensified afterbleaching by exposure to ultraviolet light. When the colorless,previously unexposed, film is intensified in a non-imagewise manner byexposure to ultraviolet light and then imagewise exposed to light ofwavelength greater than 400 nm, the resulting positive can be bleachedwith visible light, then re-intensified with ultra-violet light, andimagewise exposed with visible light without a trace of the firstexposure (i.e., no latent image). This procedure may also be repeatedmany times. It is thus seen that fatigue occurs during expo- EXAMPLE 41Dye Number 1 of Table Ill and Dye Number 23 having the formula aredissolved in pyridine and mixed with a solution of a polymer asdescribed in Example 40. The mixture of Dye Number 1 in solution isinitially colored and changes to colorless when coated or upon standing.Both the solution and coating of Dye Number 23 are pink. The coatingcontaining Dye Number 23 slowly turns dark brown at which point thecoating is relatively stable. Exposure of this coating to ultravioletlight gives little intensification and the coating does not bleach tolight of wavelength greater than 400 n. If exposures are made shortlyafter coating, the image is stable for several days to light ofwavelength greater than 400 nm, and is stable for several weeks if keptin the dark.

The following example illustrates the stabilization of 40 a photochromicsystem in either its merocyanine form or the spiropyran form by formingan insoluble metal salt or complex of the available oxygen or sulfur onthe nucleus of the merocyanine dye or by complexing the closedspiropyran.

EXAMPLE 42 A mixture of 3 X 10 mole of Dye Number 1 and l 50 X mole of aeuropium chelate salt having the formula (CH qN Eu taining Dye Number 1is purple. The solution immediately turns magenta upon the addition ofthe europium chelate salt. The mixture turns colorless when coated on asubstrate and then turns red after several days if kept in the dark.When this coating is exposed imagewise to an ultraviolet light source ofwatts, the exposed area becomes magenta. This material is faster to forman image that the corresponding polymer solution in the absence of theeuropium chelate salt and is fairly stable to tungsten light. Underconditions of normal lighting, the dye-image fades within 2-3 hours. Thecoating containing the metal chelate retains its image for many weeks ifkept in the dark whereas the same coating without the metal chelatefades in 15 minutes. The coating containing the metal chelate turns redupon heating and cannot be photobleached whereas the same coating whichdoes not contain the metal chelate rapidly turns colorless when heated.

EXAMPLE 43 Example 42 is repeated substituting Dye Number 23 forNumber 1. Separate coatings are made containing cadmium, cobalt,mercury, silver and zinc ions instead of the europium chelates used inExample 42. These coatings have an excellent image to background densityafter imagewise exposure to ultraviolet light. The dye image is stableup to one week when viewed periodically under tungsten light and theremainder of the time stored in a refrigerator in the dark. Atequilibrium, the dye exists in the merocyanine form, and after a weekstime becomes colored and blends with the image. At this point, thecoatings are stable to tungsten, ultraviolet light and heat. The colorof the coating containing the dye alone, i.e., containing no metal ions,is brown, the color of the coating containing cadmium ions is brown, thecolor of the coating containing cobalt ions is tan, the color of thecoating containing silver ions is yellow and the color of the coatingcontaining zinc ions is brown.

As used in the structural formulas herein, C H is an ethyl group and C His a phenyl group.

The invention has been described in detail with reference to particularembodiments thereof, but it will be understood that variations andmodifications can be effected within the spirit and scope of theinvention as described hereinabove and as defined in the appendedclaims.

I claim: 1. A fogged direct positive photographic silver halide emulsioncontaining at least one photographic silver halide sensitizing dyeselected from those having the formulas:

wherein a is O or 1; Z represents a heterocyclic nucleus selected fromthe group consisting of thiazoles, benzothiazoles, naphthothiazoles,thieno-[l,2-a]benzothiazoles, oxazoles, benzoxazoles, naphthoxazoles,selenazoles, benzoselenazoles, naphthoselenazoles, thiazolines,2-quinolines, 4-quinolines, 3,3-dialkylindolenines, 2-pyridines,4-pyridines, imidazoles, benzimidazoles, naphthimidazoles, andlepidines; R represents a lower alkyl group or an aryl group; and R andR each represents hydrogen, a nitro group, a halo group, a lower alkoxy'group or a lower alkyl group, provided that at least one of the groups Rand R is a nitro group or a halo group.

2. A fogged direct positive photographic silver halide emulsioncontaining a photographic silver halide sensitizing dye of the formula:

wherein a is 0 or 1; Z represents a heterocyclic nucleus selected fromthe group consisting of thiazoles,

thieno-[ 1,2-

benzothiazoles, naphthothiazoles, a]benzothiazoles, oxazoles,benzoxazoles, naphthoxazoles, selenazoles, benzoselenazoles, naphwhereina is O or 1; Z represents a heterocyclic nucleus selected from the groupconsisting of thiazoles, benzothiazoles, oxazoles, benzoxazoles,naphthoxazoles, selenazoles, benzoselenazoles, naphthoselenazoles,thiazolines, 2-quinolines, 4-quinolines, 3,3-dialkylindolenines,2-pyridines, 4-pyridines, imidazoles, benzimidazoles, naphthimidazoles,and lepidines; R represents a lower alkyl group or an aryl group; and Rand R each represents hydrogen, a nitro group, a halo group, a

lower alkoxy group or a lower alkyl group, provided that at least one ofthe groups, R and R is a nitro group or a halo group.

4. A photographic silver halide emulsion as defined in claim 1 whereinsaid sensitizing dye is l,3-diethyl- 2,3 -dihydro-6-nitrospiro( 2H l-benzopyran-2,2 -l H- imidazo[4,5-b]quinoxaline.

5. A photographic silver halide emulsion as defined in claim 1 whereinsaid sensitizing dye is 6-[( l-methylnaphtho-[l,2-d]thiazolin-2-ylidene)ethylidene]-4- nitro-2,4-cyclohexadienone.

6. A photographic silver halide emulsion as defined in claim 1 whereinsaid sensitizing dye is6[(3-ethylbenzoselenazolinylidene)ethylidene]-4-nitro-2,4-cyclohexadienone.

7. A photographic silver halide emulsion as defined in claim 1 whereinsaid sensitizing dye is6-[(l-ethylnaphtho-[2,3-dlthiazolin-2-ylidene)ethylidene]-4-nitro-2,4-cyclohexadienone.

8. A photographic silver halide emulsion as defined in claim 1 whereinsaid sensitizing dye is 6-[(3-ethyl-2-benzothiazolinylidene)ethylidene]-4-nitro-2,4- cyclohexadienone.

9. A photographic silver halide emulsion as defined in claim 1 whereinsaid sensitizing dye is selected from the group consisting of 6-[(l-ethylnaphtho[l,2-d]thiazolin-2-ylidene)ethylidene]-4-nitro-2,4-cyclohexadienone;

6-nitro-2 ,3 -dihydro-l ,3 ',3 '-trimethylspiro( 2H)- 1 benzopyran2,21H)-pyrrolo[2,3-b ]pyridine;

6-[( l ,3-diethyl-2-benzimidazolinylidene)ethylidene4-nitro2,4'cyclohexadienone;

6- 1-ethyl-4-( 1l-l)-quinolylidene)ethylidene1-4-nitro-2,4-cyclohexadienone;

6-[ 5 ,6-dichlorol,3-diethyl-2-benzimidazolinylidene)ethylidene]-4-nitro-2,4-cyclohexadienone; and

6-[ 3 ,4-diphenyl-4-thiazolin-2-ylidene )ethylidene1-4-nitro2,4-cyclohexadienone. I 10. A fogged direct positive photographicelement comprising a support having thereon at least one layer of aphotographic silver halide emulsion containing at least one photographicsensitizing dye selected from those having the formulas:

and

wherein a is 0 or 1; Z represents a heterocyclic nucleus selected fromthe group consisting of thiazoles, benzothiazoles, naphthothiazoles,thieno-[ l ,2- a]benzothiazoles, oxazoles, benzoxazoles, naphthoxazoles,selenazoles, benzoselenazoles, naphthoselenazoles, thiazolines,2-quinolines, 4-quinolines,

3,3-dialkylindolenines, Z-pyridines, 4-pyridines, imidazoles,benzimidazoles, naphthimidazoles, and lepidines; R represents a loweralkyl group or an aryl group; and R and R each represents hydrogen, anitro group, a halo group, a lower alkoxy group or a lower alkyl group,provided that at least one of the groups R and R is a nitro group or ahalo group.

11. A fogged direct positive photographic element comprising a supporthaving thereon at least one layer of a photographic silver halideemulsion containing at least one photographic sensitizing dye of theformula:

1 I Z O wherein a is or 1; Z represents a heterocyclic nucleus selectedfrom the group consisting of thiazoles, benzothiazoles,naphthothiazoles, thieno-[l,2-a] benzothiazoles, oxazoles, benzoxazoles,naphthoxazoles, selenazoles, benzoselenazoles, naphthoselenazoles,thiazolines, Z-quinolines, 4-quin0lines, 3,3-dialkylindolenines,Z-pyridines, 4-pyridines, imidazoles, benzimidazoles, naphthimidazoles,and lepidines; R represents a 22 lower alkyl group or an aryl group; andR and R is a nitro group or a halo group.

12. A fogged direct positive photographic element comprising a supporthaving thereon at least one layer of a photographic silver halideemulsion containing at least one photographic sensitizing dye of theformula:

wherein a is O or 1; Z represents a heterocyclic nucleus; selected fromthe group consisting of thiazoles, benzothiazoles, naphthothiazoles,thieno-[ l ,2- a]benzothiazoles, oxazoles, benzoxazoles, naphthoxazoles,selenazoles, benzoselenazoles, naphthoselenazoles, thiazolines,2-quinolines, 4-quinolines, 3,3-dialkylindolenines, Z-pyridines,4-pyridines, imidazoles, benzimidazoles, naphthimidazoles, andlepidines; R represents a lower alkyl group or an aryl group; and R andR each represents hydrogen, a nitro group, a halo group, a lower alkoxygroup or a lower alkyl group, provided that at least one of the groups Rand R is a nitro group or a halo group.

1. A FOGGED DIRECT POSITIVE PHOTOGRAPHIC SILVER HALIDE EMULSIONCONTAINING AT LEAST ONE PHOTOGRAPHIC SILVER HALIDE SENSITIZING DYESELECTED FROM THOSE HAVING THE FORMULAS:
 2. A fogged direct positivephotographic silver halide emulsion containing a photographic silverhalide sensitizing dye of the formula:
 3. A fogged direct positivephotographic silver halide emulsion containing a photographic silverhalide sensitizing dye of the formula:
 4. A photographic silver halideemulsion as defined in claim 1 wherein said sensitizing dye is1'',3''-diethyl-2'',3''-dihydro-6-nitrospiro(2H)-1-benzopyran-2,2''-1H-imidazo(4,5-b)quinoxaline.
 5. A photographic silver halide emulsion asdefined in claim 1 wherein said sensitizing dye is6-((1-methylnaphtho-(1,2-d)thiazolin-2-ylidene)ethylidene)-4-nitro-2,4-cyclohexadienone.
 6. A photographic silver halide emulsion as definedin claim 1 wherein said sensitizing dye is6((3-ethylbenzoselenazolinylidene)ethylidene)-4-nitro-2,4-cyclohexadienone.7. A photographic silver halide emulsion as defined in claim 1 whereinsaid sensitizing dye is 6-((1-ethylnaphtho-(2,3-d)thiazolin-2-ylidene)ethylidene)-4-nitro-2,4-cyclohexadienone.
 8. Aphotographic silver halide emulsion as defined in claim 1 wherein saidsensitizing dye is6-((3-ethyl-2-benzothiazolinylidene)ethylidene)-4-nitro-2,4-cyclohexadienone.
 9. A photographic silver halide emulsion as definedin claim 1 wherein said sensitizing dye is selected from the groupconsisting of6-((1-ethylnaphtho(1,2-d)thiazolin-2-ylidene)ethylidene)-4-nitro-2,4-cyclohexadienone;6-nitro-2'',3''-dihydro-1'',3'',3''-trimethylspiro(2H)-1-benzopyran2,2''-(1H)-pyrrolo(2,3-b)pyridine;6-((1,3-diethyl-2-benzimidazolinylidene)ethylidene)-4-nitro2,4-cyclohexadienone;6-((1-ethyl-4-(1H)-quinolylidene)ethylidene)-4-nitro-2,4-cyclohexadienone;6-((5,6-dichloro-1,3-diethyl-2-benzimidazolinylidene)ethylidene)-4-nitro-2,4-cyclohexadienone;and 6-((3,4-diphenyl-4-thiazolin-2-ylidene)ethylidene)-4-nitro2,4-cyclohexadienone.
 10. A fogged direct positive photographic elementcomprising a support having thereon at least one layer of a photographicsilver halide emulsion containing at least one photographic sensitizingdye selected from those having the formulas:
 11. A fogged directpositive photographic elEment comprising a support having thereon atleast one layer of a photographic silver halide emulsion containing atleast one photographic sensitizing dye of the formula:
 12. A foggeddirect positive photographic element comprising a support having thereonat least one layer of a photographic silver halide emulsion containingat least one photographic sensitizing dye of the formula: